1. Field of the invention
The present invention relates, in general, to a ringshaped glass bulb including a coiled filament therein. In particular, the invention relates to the ring-shaped glass bulb which is used for lamp assemblies. Lamp assemblies are used for a heating apparatus; as a heating source, or a lighting apparatus; as a light source.
2. Description of the related art
Lamp assemblies which radiate infrared rays are well known as a heating source of heating apparatus, e.g., electric stove, electric foot warmer, etc. Such an infrared ray radiating lamp typically includes a straight-shaped glass bulb wherein a filament is arranged along the elongated axis of the glass bulb. In this conventional infrared ray radiating lamp, a relatively long glass bulb is needed if the heating output of the lamp is increased. However, the increase in the length of the lamp may be restricted because of a limited space of the apparatus to which the lamp is arranged. To achieve a desired heating output in the conventional lamp, a plurality of straightshaped lamps are arranged parallel to one another. However, in this arrangement, the structure of the lamp may be complicated, and a desirable external shape of the apparatus may not be obtained.
To solve the above-described problems, the inventors of the present invention developed an infrared ray radiating lamp using a ring-shaped glass bulb wherein a coiled filament is arranged. This infrared ray radiating lamp uses a bulb material having a high temperature resistance, such as, e.g., quartz, hard glass, etc. Each end of the glass bulb at which a lead from the filament is respectively disposed is pinched to seal the bulb.
However, in this ring-shaped glass bulb, the problems which do not occur in the straight-shaped glass bulb occur when the filament is inserted into the bulb from one of the ends of the bulb, or when air in the bulb is exhausted. When the filament is inserted into the ring-shaped glass bulb from one of the ends of the bulb, the other end of the bulb opposite to the one end thereof may interfere with the filament. In particular, if a coiled filament includes a plurality of anchor portions having a relatively large external diameter, the anchor portion may be blocked by the end of the bulb when the distance between the opposite ends of the bulb is relatively small, resulting in the deformation of the filament. Furthermore, a special shaped exhausting nozzle is required to prevent the nozzle from contacting the other end of the bulb when the nozzle is inserted into the bulb from the one end of the bulb.
On the other hand, since a high temperature resistance glass material is used for the glass bulb, it is difficult to form a glass material into a desirable ring-shape. Therefore, the difference in the configuration of the opposite end portions of the bulb and variation in the dimension thereof should be taken into consideration to adapt a cap structure to the opposite end portions of the bulb.